1. Field of the Invention
The present invention generally relates to mobile communication systems, and more particularly to a system and method of controlling power of one or more mobile terminals.
2. Description of the Related Art
In a mobile communication system, power control is often used to enhance performance and minimize transmission error. In such a system, an attempt is made to adjust the transmission power of mobile terminals to be uniform. In order to accomplish this, the mobile communication system sends radio waves of low power to terminals close to a base station and radio waves of high power to terminals farther away from the base station.
The process of using a base station to adjust transmission power of a mobile terminal is called backward power controlling. During this process, the base station measures the signal-to-noise ratio of a signal received from the terminal and continuously controls backward power.
In a related-art system, the length of a frame transferred to the base station through a backward traffic channel is typically 20 ms and a power control period of the base station is usually 1.24 ms. With this frame and period, the base station is able to perform backward power control 16 times. Each time interval during which backward power control is performed may be referred to as a power control group (PCG).
The related-art backward power control method as performed by the base station will now be described. When frames of a terminal arrive, the base station measures the signal-to-noise ratio (referred to as ‘PCG_(Eb/No)) of each PCG, and compares the measured PCG_(Eb/No) with a pre-set reference Eb/No. If the PCG_(Eb/No) is smaller than the reference Eb/No, the base station increases backward power (transmission power of the terminal). However, if the PCG_(Eb/No) is greater than the reference Eb/No, the base station generates a power control signal for reducing backward power and transmits this signal to the terminal. Then, the terminal increases or decreases its transmission power with reference to the power control signal.
The power control signal has a total size of 6 bits, including 4 bits for power control position designation and 2 bits for power controlling. If the power control bits are ‘00,’ the terminal decreases its transmission power to achieve a prescribed strength. If the power control bits are ‘11,’ the terminal increases its transmission power to achieve a prescribed strength.
Backward power control is continuously performed while the terminal transmits signals. However, the related art power control method has at least the following problem. Because the base station transmits a power control signal to the terminal even in a situation where signal quality of a backward channel is stably maintained (e.g., in a situation where power control is not necessary), the opportunity or availability of transmitting data information (such as a voice signal) at least at a desired rate is limited. As a result, transmission efficiency of the backward channel is substantially degraded.